Names of `stringp`, `intp`, `flo atp`…

Just out of curiosity, what does the "p" means in `stringp`, `intp`,
`floatp`, `functionp`, `objectp`, `arrayp`…?
 
When I found those useful functions by the first time, I wondered why
they were not called, say, `is_string`, `is_int`, `is_float`,
`is_array`…?

-- 
Marcos Cruz
http://programandala.net